Vacuum-tube repeater



Patented den. i6, i923.

41unritrae stares ROBERT C. MATHES, OF NEW YORK, 1\T. Y., ASSIGNOB TO WESTERN ELEOTRC OOM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATXON OF NEW YORK.

VACUUM-TUBE REPEA'IER.

Application filed November 4, 1916. Serial No. 129,116.3.

' To all ywhom if may con-cern.

Be it known that l, ROBERT C. Marinas, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful improvements in Vacuum- Tube Repeaters, of which the following is a full, clear, concise, and exact description.

This invention relates to vacuum tube repeaters, in which a variable source of potential, such as a storage. battery, is provided for the `plate or output'circuit, and has for its object to provide method and means for minimizing the variations in amplifying power due to the inconstancy of the potential of the source.

A further object of the invention is to lprovide a. method and means for preserving the impedance balance in case it is necessary to use a transformer having a ratio not suitable to the normal impedances at opposite sidesthereof, and in general to improve the transmission of alternating currents through a vacuum tube repeater or amplifier.

The alternating current in the output circuit of the vacuum tube depends uponthe sum of the internal impedance of the tube and the impedance in that portion of the output circuit external to the tube. The change in amplifying power is due to the variation of the internal impedance of the tube with the change in value of the supplied potential.

The invention provides for. making the external impedance larger than the internal impedance whereby the percent of variation in the impedance of the output circuit is, as a whole, reduced, and the amplifying power is made more nearly constant. The transfer of energy from a tube to its external circuit is a maximum when the internal and external impedances are equal,

and in increasing the external impedance to steady the amplification, the relative amount transferred is4 reduced. It is necessary to strike a balance between the variation in amplification due to an unsteady source andY the amount of amplification.

The desired value of the external impedance may be secured by choosing a proper ratio of transformation for the transformer coupling the vacuum tube to the external circuit. lf the transformer has N1 primary, and N2 secondary turns, and if there be an impedance Z2 in the secondary circuit, the impedance of this system as a whole is equivalent to an impedance e, in the pri- A impedance .al is known the equivalent primary impedance, and constitutes all or a part of the external impedance in the output circuit of the tube. By Vassigning the proper values to N1 and to N2, the equivalent primary impedance may be given any desired value for any specific value of the external impedance Z2.

mary circuit of value el:

N,\2 .ln case the iatio is increased to ratio or Nv is correspondingly reduced.

it is-another object of the invention to offset `the reduction in the impedance of the repeater set consequent upon an increase in the equivalent primary impedance due to a change in the ratio of transformation. This is accomplished by inserting a resistance in circuit with the transformer.. By using a proper amount of the resistance inserted in circuit with the transformer, the impedanceI of the repeater set may be restored to its former value or it may be given any other desired value. lf, for example, as often is the case in practice, it is desirable to match the impedance of the repeater set with the impedance of the line, such a resistance is inserted that the resultant impedance of the primary circuit of the transformer when multiplied by the transformer ratio is substantially equal to :the impedance of the secondary circuit. By .transformer ratio is meant the square of the ratio of turns in the transformer windings.

This will be further considered in connectio-n with the drawings, in which:

Figures l and 2 disclose repeating systems; and Figure 3 shows a set of curves A giving the relation between the miles gain and the percent of normal B voltage for various ratios between the external and iny ternal impedances, for the system shown in Figure 2.

Figure 4 shows a modification in which a resistance may be inserted in the secondary 'circuit ofthe transformer instead of in the primary circuit as shown in Fig. 2.

In Figure l, the repeater l is a threeelement vacuum tube of the audion type in which the grid l0 is maintained at a suitable potential by the battery 11. The B battery 2 in the output circuit is a source of inconstant potential, such as a storage bate tery, which supplies the Space current to the tube through the impedance 7. The condenser 8 passes alternating current but prevents directcurrent from battery 2 from being supplied to transformer 3. The output circuit ofthe tube 1 comprises the prrmary windingof transformer -3,"the secondary Winding'of which supplies an impedance Z2 which conventionally represents Atheimpedance of a line in which the repeater is connected. This repeater is adapted to repeat without distortion, that is, itA

provides a faithful reproduction of the currents which it handles in contradistinction to operating as a detector orrectier.

Looking in the direction a from line 5 there is encountered the internal impedance Ro of tube l; in the direction b there is the external impedance or the impedance in the output circuit which is external to the tube. The impedance measured at the line 6 in the direction c is the impedance at the secondary side of the transformer 3 or is the impedance of the repeater set. The impedance AZ2 is found on looking in the direction d from the line 6.

A so-called standard set is one in which the impedance as measured in 'one direction from line 5 equals the impedance as measured in the other direction therefrom; and equal impedances are measured in either direction from line 6. When the transformer is such as to fulfill these conditions, there is the maximum transfer of energy from the vacuum tube into the line. i

Consider such a standard set in which the impedances looking in both directions from line 5 are equal, i. e., the internal and external impedances are equal. The equivalent primary impedance -of the standard set is RS= LZ2 where a= %)z. In Vorder to 2 Y make the equivalent primary impedance larger, the ratio of transformation is changed by making either N,L larger or N2 smaller, or by making both-N1 larger and N2 smaller. Suppose that the number of turns of the transformer windings have been assigned new values N11 and- N21 respectively, such as to now make the equivalent primary impedance n times that of the former value. The new value R51 of the equivalent primary impedance is B1=a1Z2 where a1= 2 Since n is defined as being the ratio of the two values of' the equivalent primary impedance n= --E2-= E- v Of course in the standard set al =a and n= 1.

In changing the ratio of transformation to increase the equivalent impedance on the primary side of the transformer, the impedance of the repeater set .as-seen in direction C tion of n If the impedance as measured on the secondary side of the transformer, or as measured in the direction. c fromthe line 6, has.'

been reduced below the value which it should have in order that the system may function .properly when the repeater set is connected to the' impedance Z2, then the impedance in direction c from the line 6` may be raised to 100 its proper value by inserting the proper amount of resistance 4 in the primary clrcuit of transformer 3, as shown in Fig. 2. Assuming that the coil ratio has been changed rso that the equivalent primary impedance is n. 'times its former or standard value Ro, then the impedance of the set, i.`e., the impedance looking in the' direction c from line 6, is restored to its former value by inserting a resistance of the value (n-1)Ro in the primary circuit. Or a resistance of proper value may be inserted inthe secondary circuit of the transformer, as shown in Fig. 4. While the insertion of a resistance introduces some additional impedance, it also serves to further diminish the fluctuations in gain by adding to the impedance external'to the vacuum tube. If, after the coil ratio has been changed, it is not desired to assign a particular'impedance value to the set, the resistance element may be omitted, as shown in Fig. 1. l I

Reference -is 'now made to Fig. 3 which shows .how the amplification or miles vgain varies when a variable source of potential .is used in the output circuit of the tube, as shown in Fig. 2. By miles gain is meant the length `inl miles that a telephone line may be increased by reason of the presence of the amplifier, a given intensity of current being delivered at the end of the line. From Fig. 3 it is seen that when 71:1, the miles gain varies from 19.5 to 22 for the maximum variation in voltage when a storage battery, subject to charge and discharge, is used in the plate circuit. rl`he absolute .values of gain here given are arbitrary and depend upon the particular design of theI repeater set. The numerical differences, however, are the same for all values of total gain. v1f the N2 shown in Fig. 3, the variation in miles g'ain or amplification is reduced, but the actual gain is however reduced. By further increasing the value of n, the variation in gain or amplification is correspondingly reduced. The factors of diminished gain and constancy of gain resulting from these changes must be balanced to meet the requirements of any particular case.

The ratio of the external to the internal impedance of the system shown in Fig. 2 is (2n- URO R0 of this ratio for the different values of a for which the curves are plotted. As indicated opposite the three lowercurves, when n is given values of 2, 3, and 4, the external impedances have values of three, five, and seven times the internal impedances, respectively.

In making the external impedance large as compared to the internal impedance when a fluctuating source is used, this system also has the advantage present in the system disclosed in the application of Arnold, Serial ratio is so increased that n=2, as

Fig. 3 shows the various values No. 85,362, filed March 20, 1916, in which-a straight li'ne characteristic is secured for the amplifier by makingthe -external impedance comparable to the internal impedance of the amplifier.

lhat is claimed is:

1. The method of reducing the variations in amplifying power of a repeater with variations in the voltage of a local source of energy associated therewith, which consists in impeding the output current externally of said repeater to a greater extent than said current is impeded internally of said repeater, thereby repeating without distortion.

2. The method of reducing the variations in amplifying power of a repeater with variations in applied direct current voltage, which 4consists in impeding the current'eX- ternally of said repeater to a greater extent than said current is impeded internally of said repeater, thereby repeating without distortion.

3. The method of reducing the variations in amplifyingpower of a vacuum tube repeater with variations in applied direct current voltage, which Consists in impeding the current externally of said tube to a greater extent than said current is impeded internally of said tube, thereby repeating Without distortion.

i. The method wherein is employed a vacuum tube repeater coupled to an external circuit by means of a transformer, which comprises providing for said transformer a ratio of transformation such that the equivalent external impedance in the out-put circuit of said tube is larger than the internal impedance of said tube.

5. The method wherein is employed a vacuum tube repeaterihaving an output circuit and a transformerrin said output circuit, 4which comprises providing for said transformer a ratio of transformation such that the equivalent externa'l vimpedance in the output circuit ofsaid tube is larger than the internal impedance of said tube, and in impeding the currents in said output circuit to give said repeater set a desired impedance'.

6. The method wherein is employed a vacuum tube repeater coupled to an outgoing line, which comprises impeding the out-put current externally of said repeater to a. greater extent than said current is impeded internally of said repeater, thereby repeat infr without distortion.

'1. rihe combination of avacuum tube repeaater having an output circuit, a variable output source of potential therefor. and a impedance in the output circuit of said tube, said impedance having a value greater than that of the internal impedance of said tube, whereby said repeater is adapted to repeat without distortion.

8. rThe combination of a vacuum tube repeater, a source of variable potential for the output circuit the-reef, and a. translating systemv supplied with power by said tube, said translating system having an equivalent im- Ypedance larger than the internal impedance of said tube, said translating system come prising a transformer and an impedance energized thereby.

9. The combination of a vacuum tube of the audion type, a space current source of variable potential for said tube, a transformer having primary and secondary windings,ymeans for supplying power to said primary winding from said tube, an imped ance supplied with power by said secondary winding, the ratio of transformation of said transformer being such as to give the outputimpedance external to said tube a value larger than that of the internal impedance of said tube, and-means for giving the impedance at the secondary side of said transformer adesired value.

10. The combination of a vacuum tube ofiy the audion type, a space current source of pedance of said tube, and a resistance in circuit with said primary winding.

11. In combination, a transformer comprisingv primary and secondary windings, an impedance element associated with the sec' ondary winding of the transformer, a transmission cir'cuit associated with the primary winding of the transformer', and means associated with the primary c ircuit whereby the resultant impedance of the primary circult when multiplied by the transformer ratio is rendered substantially equal to the secondary impedance.

12. In combination, a transformer comprising primary and secondary windings, an impedance element associated with the secondary winding of the transformer, a trans mission circuit associated with the primary winding of the transfor1ner, and an impedance element between said transmission circuit and transformer, said last mentioned impedance element being so proportioned that the resultant impedance of the primary circuit when multiplied by the transformer ratio is substantially equal to the impedance of the secondary clrcuit.

13. An arrangement to associate circuits Vof unequal impedance comprising a transformer, and (n impedance element in the primary circuit of the transformer so proportioned that the resultant impedance of the primary circuit when ymultiplied by the transformer ratio is substantially equal to the secondary impedance.

14:. An arrangement to associate circuits of unequal impedance comprising a transformer,- and an impedance element in the primary circuitof the transformer so proportioned with reference to the transformer ratio and the impedance connected across the secondary terminals of the transformer that the resultant impedance of the primary circuit when multiplied by the transformer ratio is substantially equal to the secondary impedance.

15. In combination, prising primary and secondary a windings,

circuits associated with each of said windings, and means associated with one of said windings whereby the resultant impedance of one of said circuits 1s rendered Substan tially equal to the impedance of the other circuit multiplied by the transformer ratio.

16. In combination, va vacuum tube re- I peater having an output circuit, a second voutput circuit connected a transformer com# circuit, a transforme-r coupling said circuits, and means associated with one of Said circuits whereb-y the impedance of one of said circuits is rendered substantially equalto the impedance of the other of said circuits multiplied by the transformer ratio.

17. In combination, a vacuum tube repeater having an output circuit, a second cir-` cuit, a transformer coupling said circuits, and a resistance serially connected in one of said circuits said resistance being of such a value that the impedance of one of said circuits is rendered substantially equal to the impedance of the other of said circuits mulf tiplied by the transformer ratio.

18. The combination of a vacuum tube of the audion type, a space current source of variable potential for said tube, a transformer having primary and seconda-ry windings, means for supplying current to said primary winding from said tube, an impedance supplied with current by Said secondary winding. the ratio of transformation of said transformer being such as to give the output impedance external to said tube a"A value larger than that ofthe internal impedance of said tube. a resistance in circuit with sa-id primary winding', said resistance being' of such a value that the impedance of the primary circuit when multiplied by the transformer ratio is rendered substantially equal to the impedance of the secondary circuit.

19. The method of transmitting currents through a transmission System, which comprises transforming said currents at a ratio tending to unbalance the impedance equality of the system adjacent the point of transformation and substantially restoring the impedance balance Aby impeding the currents at one side of the point'of transformation.

20. The method of ballasting an electric translating device the internal impedance of which varies with the applied voltage, which comprises making the external impedance of said device large as compared with the normal internal impedance, thereby rendering the effect of said variations negligible.

21. A. thermionic repeater having cathode, anode and control electrodes, means for supplying current between said cathode and anode, means connected to said cathode and control electrode for impressing thereon alternating currents to be repeated, and an to said cathode and anode, said output circuit comprising a transformer and a work circuit, the ratio of transformation of said transformer being of such a value that said output circuit has an impedance larger than the impedance between cathode and anode.

22; A thermionic repeater having cathode, anode and control electrodes, plying current between said cathode and anode, means connected to said cathode and me-ans for supimpedance of the order of five times the impedance between cathode and anode.

In witness whereof, l hereunto subscribe lo my name thislst day of November A. D.. 1916. v

ROBERT C. MATHES. 

